In the image pickup apparatus, when an object is displayed on the screen of a display, a scale is displayed in juxtaposition on the screen such that the size of the object can be recognized easily.
In this case, when an optical magnification of a lens is constant, it may suffice to display a scale of a predetermined size but, in a case of using a variable magnification lens such as a zoom lens, it is also necessary to change the size of the scale in accordance with the magnification.
In such existent image pickup apparatus, it has been adapted to detect the position of a magnification adjusting movable lens and a varifocal movable lens used in a zoom lens, calculate the optical magnification of the lens based thereon, and set the size of the scale.
[Patent Document 1] JP-A No. 10-210327
However, in an image pickup apparatus of high magnification used as a microscope, since the focus is adjusted by relative movement of a stage in the direction of the optical axis, the lens has no varifocal movable lens and since the lens of high magnification has an extremely shallow depth of field and the object distance is primarily determined, so that it is not necessary to detect the same.
In view of the above, it has also been proposed an image pickup apparatus of reading a positional information of a lens based on output signals from a driving section for a magnification adjusting movable lens, calculating the magnification and setting the scale.
[Patent Document 2] JP-A No. 2000-155268
However, since a lens includes a magnification error of about 5% in a fixed focal length lens and about 10% in a zoom lens, in a case where it is intended to detect the magnification based on output signals from the driving section for the magnification adjusting movable lens, it inevitably contains an error of about 5 to 10%.
Further, since the positional information of the magnification adjusting movable lens is outputted from a zoom lens in any case and the magnification is detected based on the positional information in an image pickup apparatus main body, it is necessary to store data inherent to the lens necessary for converting the positional information into the magnification on the side of the image pickup apparatus.
In this case, since there is only one kind of data inherent to the zoom lens to be used in the existent image pickup apparatus not capable of lens exchange, it may suffice to merely store the data thereof.
However, in a case of using an image pickup apparatus as a microscope, it has been demanded that observation can be conducted under an appropriate magnification over a wide range of factor, for example, from several to several hundreds times depending on a body to be observed (object), and the range capable of controlling the enlarging magnification with only one zoom lens is restricted and the magnification can not be set freely.
Further, there is also a demand of using various kinds of lenses while exchanging them such that lenses of optional optical characteristics can be used selectively.
In this case, the demand can be satisfied by using an image pickup apparatus capable of lens exchange. However, since the data inherent to the lens are different in a case of calculating the magnification based on the positional information of the lens respectively upon exchange of lens, the enlarging magnification can not be calculated.
Further, in a case of a magnification fixed lens, since a magnification controlling variable lens is not present, the enlarging magnification can not be calculated based on the positional information.
Accordingly, it has been difficult to display a scale indicative of a reference length at an accurate length on a screen.